The invention relates to an inner lining for tanks containing liquids, in particular gasoline tanks, comprising an intermediate layer which can be placed against the tank wall end which is air-permeable and electrically conductive, and a gasoline-resistant inner envelope resting on the intermediate layer. The invention is also concerned with a tank, particularly a gasoline tank, which is provided with such an inner lining.
Known inner linings and tanks of this type (DE 76 17 733 U1) have an electrically conducting intermediate layer or a liner made of a metallic nonwoven fabric, for example special steel wool, and an inner envelope or insert made of a gasoline-resistant material, for example nitrile caoutchouc. The intermediate layer is pervious to air and is used to maintain a minimum distance between the inner envelope and the tank wall, even if a vacuum is provided in a known manner between the inner envelope and the tank wall which, on the one hand, assures the tight adherence of the inner envelope against the tank wall and on the other hand makes a check for leaks possible.
The interior envelope is diffusion- or liquid-proof and in contrast to the PVC foils used in connection with heating oil, resistant to the gasoline to be stored. However, because it is made of nitrile caoutchouc it has several disadvantages. Since nitrile caoutchouc is a rubber-like elastic material, the inner envelope is not very well suited for tank construction, where foils are preferred, which are as easily bendable as possible, can be easily fabricated and can be welded by customary means. Furthermore, the backs of such inner envelopes are grounded via the intermediate layer. But since they are made of a material with high volume and surface resistance, the front side which comes into contact with the gasoline is not sufficiently antistatic.
This has the result that there is a danger of explosions because of unavoidable build-ups of electrical charges. Dangers of this type exist in particular when walking through a gasoline tank provided with such an inner lining, because it is then possible that sparks can be generated by frictional electricity.
Because of these deficiencies of known inner linings, no inner linings of the species recited at the outset are used today in connection with tanks for gasoline and other flammable or explosion-prone liquids. Such inner linings have not been approved an far by the competent supervisory authorities in particular, especially since the respective regulations are different. For example, on the one hand inner envelopes made of foils of a thickness of no more than 2 mm are required in connection with gasoline or the like, because supposedly ignition of materials of the explosive groups IIA and IIB in not expected up to these thicknesses. On the other had, for preventing the danger of ignition because of electrostatic charge build-up it is demanded that it must be assured by the addition of carbon black or the like, that the surface or conduction resistances are not allowed to exceed 10.sup.9 or 10.sup.8 Ohm at any place (Employers' Liability Insurance Association of the Chemical Industry, Guideline No. 4 ZH 1/200 "Static Electricity", October 1989).
Up to now, the mentioned regulations could not be met by inexpensive foils which can be processed in the customary manner in tank construction. For this reason, it is still customary today to store gasoline and similar explosive materials, for example kerosene, in double-walled tanks made of steel or the like, whose interior walls as a rule are provided with expensive, health-endangering interior layers of polyester resin or the like. For this reason the constructive and therefore also the financial outlay for producing gasoline tanks or the like in considerable.